(1) Field of the Invention
The present invention relates to propulsion systems for marine vehicles and more particularly to electromagnetic thruster systems.
(2) Description of the Prior Art
It is well known that when an electric current is passed through a wire or any other conductor placed in a magnetic field, an electromagnetic force, referred to as a Lorentz force, pushes the wire in a direction perpendicular to the wire and the magnetic field. Applying this law of physics to electromagnetic propulsion systems, the conductor of electricity is seawater instead of a wire. An electric current is passed through the seawater by the use of high current density seawater electrodes. The electrodes are positioned such that the electric current flows at right angles to the magnetic field generated by the electromagnets. Hence, a Lorentz force is produced which acts against the conductive seawater which, in turn, is pushed backward, propelling the ship, submarine or torpedo forward. This principle of electromagnetic propulsion was described in detail in U.S. Pat. No. 2,997,013, issued to Warren A. Rice on Aug. 22, 1961.
However, practical applications of prior electromagnetic propulsion systems have been limited by water's low electric conductivity and by the relatively low maximum available magnetic flux density of approximately 0.6 Telsa (T). In 1979, Hummert conducted an evaluation of a DC electromagnetic thruster (EMT) in seawater. Hummert's results revealed the possibility of EMT increased efficiency if the magnetic flux density could be increased to 5T. In 1983, studies conducted by Japanese scientists, Tada and Saji, concluded that only a breakthrough in superconductivity would bring about advances in electromagnetic propulsion.
Recent advances have been made in two areas, both of which improve the practicality of electromagnetic thrusters. First, superconducting materials are available with critical temperatures increased from four degrees Kelvin (4.degree. K.) to ninety-eight degrees Kelvin (98.degree. K.); second, the critical magnetic field strength has been raised from 12T to 70T. These developments are indicators of promising increases in the efficiency of an electromagnetic thruster.